Coal processing

ABSTRACT

A method and apparatus for removing moisture from coal and for comminuting coal.

United States Patent Chapman 1451 Aug. 1, 1972 [541 COAL PROCESSING 3,477,941 11/1969 Nelson ..208/8 [72] inventor: Robert R Chapman, Lafayette m 3,381,388 5/ 1968 Chakravam et a1. ..34/9 p 3,518,773 7/ 1970 Johanson ..34/26 3,520,067 7/1970 Winegartner ..34/9 [731 Asslgm= many, New 2,929,150 3/1960 Johnston ..34/9

York, NY.

[22] Filed: 1970 Primary Examiner-Frederick L. Matteson [2]] App] 2,735 Assistant Examiner-W. C. Anderson Attorney-Blucher S. Tharp and Roderick W. Mac- D 1d 52 us. c1. ..34/9 [51] Int. Cl ..F26b 58 Field 61 Search ..34/9, 73, 61, 69, 36, 15; 1571 ABSTRACT 208/8 A method and apparatus for removing moisture from [56] References Cited coal and for comminuting coal.

UNITED STATES PATENTS 5 Claims, 1 Drawing Figure 6/1967 Lamb et a1 ..34/9

I HEATED SLURRY MEDIUM THICKENED COAL SLURRY PATENTEDAIJK 1 I972 3.680.217

LIQUID WATER WET COAL 4 HEATED 4 4 SLURRY MEDIUM THICKENED COAL SLURRY INVENTOR ROBERT F. CHAPMAN lzwwm/w ATTORNEY COAL PROCESSING BACKGROUND OF THE INVENTION Heretofore wet coal coming from the coal mine or washing plant associated with the coalmine has been dried by simply forcing hot air or hot flue gas over the coal without recovery of the water removed from the coal.

It has also been disclosed in U. S. Pat. Nos. 3,518,773, and 3,519,552 to use vent gas from a coal hydrogenation process or a gas formed from steam or aliphatic or aromatic hydrocarbon to dry coal. The vent gas from a coal hydrogenation process contains substantial amounts of gases such as hydrogen, carbon monoxide, carbon dioxide, methane, ethane, and propane which are very difficult to condense and in some cases are referred to as non-condensables. It is difficult to substantially dry a material using steam and when using steam or aliphatic or aromatic hydrocarbons some non-condensables are picked up. When the gas is then reused in the drying step these non-condensables are also re-introduced into the drying step.

It has also been disclosed in U. S. Pat. No. 3,520,067 to dry coal by passing same through a pool of heated liquid oil, the pool of oil being fixed in place with the coal passing therethrough and only a slight amount of oil being removed from the pool with the dried coal.

In the mining of coal, a substantial amount of mining is carried out in arid regions where the conservation of water is a necessity to the economical operations of the mine and any coal washing operation.

Therefore, it is important that in the drying or even partial removal of moisture from wet coal, that the process be carried out in a manner such that the maximum amount of water after removal from the coal can be recovered for reuse.

SUMMARY OF THE INVENTION It has been found that non-condensable, inert, and/or fixed gases such as nitrogen, carbon dioxide, and the like carry substantial amounts of water vapor with them through a water vapor condenser and that maximum water recovery together with maximum efficiency in subsequent coal hydrogenation and liquefaction processes is achieved by employing, as a drying gas, a hydrocarbonaceous liquid slurry medium previously obtained from a coal hydrogenation liquefaction process.

Because the slurry medium used as a drying gas of this invention has previously been through a process of coal liquefaction it has substantially no non-condensables or inert or fixed gases which impede condensation of all water vapors removed from the wet coal. Additionally, because of its coal derivation, the slurry medium is very compatible with coal and can be employed as the carrier medium in a subsequent coal liquefaction process. Therefore, there is no need for removing the slurry medium of this invention after the drying operation is completed. In fact, it is much more desirable and efficient to leave the coal in the slurry medium for subsequent transportation, processing, and the like.

Thus, by this invention drying of coal with a wet gas such as steam or gas containing non-condensables which impede water vapor condensation, or drying with a large fixed bed of hot oil, are eliminated while at the same time greater recovery of water is achieved because the water vapor removed from the coal by the process of this invention is substantially only water vapor and can be substantially percent condensed for reuse as needed.

This is particularly desirable when mining is carried out in arid regions.

In addition, there is the distinct advantage that the coal/slurry medium mixture issuing from the drying step of this invention is already suitable for use in coal liquefaction processes such as, for example, hydrogenation in an ebullated bed process which is fully and completely disclosed in U. S. Pat. No. Re 25,770, the disclosure of which is incorporated herein by reference.

The above method of this invention can be further modified in accordance with this invention so that the coal/slurry medium mixture produced by this invention can be treated in a conventional manner to remove part of the slurry medium for reuse in drying fresh wet coal thereby producing a thickened slurry more suitable for transportation and the like.

Additionally, it has been found advantageous to comminute the coal in the presence of the slurry medium so that at one or more places after the mixing of slurry medium and coal, the mixture can be subjected to a coal comminution step. By grinding the coal in the presence of the slurry medium which is also employed in subsequent liquefaction processes for the coal, freshly exposed surfaces of the coal are protected from oxidation and the like so that more reactive coal particles are supplied to the liquefaction operation.

This invention also relates to an apparatus for at least partially drying coal which employs means for mixing wet coal and slurry medium followed by flash means for vaporizing at least part of the water from the resulting mixture of coal and slurry medium. There can also be employed a grinding means between the mixing means and flash means and/or downstream of the flash means. Additionally, thickening means can be employed on the coal/slurry medium mixture issuing from the flash means and grinding means can be employed downstream with the thickening means if desired.

Accordingly, it is an object of this invention to provide a new and improved method and apparatus for at least partially drying coal. It is another object to provide a new and improved method and apparatus for drying and comminuting coal. It is another object to provide a new and improved method and apparatus for removing water from wet coal in a manner which renders the water vapor removed from the wet coal substantially completely condensable for recovery and reuse while also dispersing the coal in a compatible liquid medium which can serve as a slurry medium or solvent in a subsequent coal liquefaction process.

Other aspects, objects, and advantages of this invention will be apparent to those skilled in the art from this disclosure and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION The drawing shows apparatus representing one embodiment of this invention.

More specifically the drawing shows heated gaseous slurry medium (solvent) in pipe 1 being supplied to an eductor means 2 which receives wet coal from pipe 3 for mixing therewith.

The resulting coal/slurry medium mixture, still undergoing mixing, is passed by way of pipe 4 to flash means 5 wherein the mixture is subjected to flash conditions including a temperature above the vaporizing temperature of water at the flash conditions but below the vaporizing temperature of the slurry medium so that substantially only water vapor is removed from flash means 5 by way of overhead pipe 6. The water vapor then passes through conventional condenser 7 and substantially all the vapor condensed to liquid water which is transported by pipe 8 to any desired place for reuse such as in a coal washing step upstream of pipe 3.

The at least partially dried coal now dispersed in the slurry medium is removed as underflow in pipe 10 and can be transferred as such for further processing including liquefaction of the coal.

If desired, the slurry can be thickened by passing to separator means 11 which separates a part of the liquid and/or gaseous slurry medium from the coal so that substantially only slurry medium is removed overhead by way of pipe 12. This removed slurry medium can be reheated by heater 13, if desired, and then passed by way of pipe 14 for reuse in pipe 1. The thickened slurry medium is removed by way of pipe 15 for transportation, coal liquefaction, and the like.

If desired, a coal comminuting or grinding operation can be carried out at one or more places after mixing of the coal with the slurry medium. For example, a comminuting operation canbe carried out between mixing means 2 and flash means 5 as represented by 16, downstream of flash means 5 as represented by 17, downstream of thickener 11 as represented by 18, or any combination of two or more thereof.

Mixing means 2 can be the vacuum type eductor shown in the drawing or any other suitable mixing means such as conventional batch or continuous flow mixers so long as the desired result of intimate mixing of the subdivided wet coal in pipe 3 with the heated slurry medium of pipe 1 is achieved.

Flash means 5 can be any conventional equipment which operates at ambient or sub-ambient pressures and which can be heated to the desired temperature above the boiling point of water and below the minimum boiling point of the slurrying medium under the pressure conditions obtaining in the flash means 5.

Condenser 7 can be a water or air cooled condenser, with baffle means and the like if desired, and which simply cools the water vapor from pipe 6 and condenses same to form substantially only liquid water for pipe 8.

Thickener 11 can be any conventional thickener which by way of gravitation, centrifugation, filtration, or similar operations separates the coal particles from a portion of the slurry medium. Removal of a portion of the slurry medium from the coal particles can be achieved by vaporization and/or condensation of a portion of the slurry medium. If theslurry medium is removed by vaporization, heater 13 may be omitted. On the other hand if separation is achieved by condensation heater 13 may be necessary.

According to the method of this invention a hydrocarbonaceous liquid slurry medium obtained from coal liquefaction is employed as a source of the drying gas. The slurry medium is preferably a hydrocarbonaceous liquid obtained by the hydrogenation of normally solid particulate coal at a temperature of from about 500 to about l,0O0 F. and under a pressure from about 400 to about 500 psig. Hydrogenation can be carried out in the presence of hydrogenation catalyst particles, substantially inert solid contact particles, or combinations thereof. The hydrogenation can also be carried out in an empty reactor in that there are no externally supplied contact particles initially present in the reactor. The primary goal is that of liquefaction of the coal to produce, at least in part, a liquid hydrocarbonaceous product. This can readily be ac complished by the apparatus and process disclosed in U. S. Pat. No. Re 25,770.

Generally, the coal, subdivided so that at least about weight percent thereof passes an 8 mesh (Tyler) sieve, is subjected to a total pressure from about 400 to about 5,000 psig at a temperature of from about 500 to about 1,000 F. together with sufficient hydrogen gas to provide a hydrogen partial pressure of from about 350 to about 3,000 psia. A coal derived slurry medium (solvent) is mixed with the particulate coal before being subjected to liquefaction and is generally added to the coal to provide a slurry medium/coal weight ratio of from about 0.1/1 to about 5/1. lf inert or catalytic contact particles are employed in the process they can be subdivided to be within the size range of from plus 200 mesh (Tyler) to one-fourth inch. Fresh catalyst can be added at the rate of at least about 0.1 pounds of fresh catalyst per pound of coal process. The coal is normally charged in the amount of from about 15 to about 200 pounds of coal per hour per cubic foot of reactor.

The coal liquefaction process generally produces a gas which is composed primarily of methane, ethane and propane, liquid products such as naphtha, light distillate, heavy distillate, and heavy fuel. The liquid product before fractionation generally ranges from butane to hydrocarbonaceous materials boiling at about l,500 F. A portion or any fraction of this liquid product can be employed as the slurry medium for this invention since the entire liquid and any fraction or portion thereof is a coal derived hydrocarbonaceous liquid. Generally, the particular material chosen as the slurry medium for this invention should boil at a higher temperature than water under the same pressure conditions so that in flash means 5 water will be vaporized while the slurry medium is not.

The slurry medium is heated to a temperature sufficient to vaporize same and then supplied by way of pipe 1 to mixing means 2. Wet particulate coal which can have substantially greater than 50 weight percent water associated therewith and which can be preheated to a temperature above ambient or can simply be at ambient temperature is supplied by way of pipe 3. The coal and heated slurry medium are preferably supplied in amounts sufficient to provide a slurry medium/coal weight ratio of from about 0.5/ l to about 5/1.

Thereafter the resulting mixture is passed to a flash zone and subjected to conditions of super-ambient, ambient, or sub-ambient pressure and elevated temperature above the boiling point of water but below the boiling point of slurry medium so that water is vaporized and slurry medium condensed thereby removing water from the coal and forming the desired coal/slurry medium mixture.

Sometimes it is desirable to substantially completely dry the coal. Other times it can be desirable to charge coal having a certain amount of moisture associated therewith to a coal liquefaction process Therefore, the coal is maintained under flash conditions for a time suf ficient to remove moisture down to the desired level if not to remove substantially all the moisture from the coal. It can be desirable for the coal to have associated therewith about 0.1 to about 50 weight percent water for certain coal liquefaction processes. Therefore, the coal can be maintained under flash conditions for a time sufficient to remove substantially all the water therefrom or at least to remove water to the point where the coal being removed from the flash zone has associated therewith from about 0.1 to about 50 weight percent water based on the total weight of the coal.

Generally, when the flash pressures are ambient or sub-ambient, a temperature of from about 150 to about 450 F. can be employed in the flash zone when I the slurry medium is composed of hydrocarbonaceous materials ranging from light distillates to hydrocarbonaceous materials boiling at about 1,500 F.

The water vapor removed from the flash zone will be substantially all water vapor and will contain substantially no hydrogen, carbon monoxide, carbon dioxide, hydrocarbons such as methane, ethane, propane, and the like so that substantially 100 percent of the water vapor removed from the flash zone can be condensed to the liquid state by conventional condensers operating substantially at or near ambient temperatures. Thus, substantially 100 percent water recovery is achieved without the requirement of elaborate water condensation equipment or processes.

EXAMPLE Illinois No. 6 coal subdivided to all pass through a mesh sieve (Tyler) and having associated therewith about 8 weight percent water based on the weight of the coal is provided in pipe 3 while a slurry medium composed of a hydrocarbonaceous oil having a boiling range of from 500 to 975 F. and obtained from the same Illinois No. 6 coal by hydrogenating same with molecular hydrogen at a temperature of about 850 F. and hydrogen partial pressure of about 2,250 psia is heated to about 1,100" F. and provided in pipe 1.

The heated slurry medium and wet coal from pipes 1 and 3 and recycle slurry medium from pipe 14 are mixed at rates which provide a slurry medium/coal weight ratio in eductor 2 of about 3/1 and then passed to a flash unit 5 which is maintained at a pressure of one atmosphere and a temperature of 280 F. Coal residence time in the flash unit is about 30 minutes.

Water vapor removed from the flash unit at pipe 6 is substantially completely condensed to liquid water with a water cooled condenser maintained at about F. A coal/slurry medium mixture is removed from the flash unit by way of pipe 10 wherein the slurry medium/coal weight ratio is substantially 3/1 and the coal has associated therewith about 1 weight percent water based on the weight of the coal.

This mixture is thickened in a Dorr thickener unit 11 which allows the mixture to come to a quiescent state and the solid coal particles settle to the bottom thereof. Substantially solid free hydrocarbonaceous oil is decanted from the top thereof into pipe 12. A thickened coal slurry is removed by way of pipe 15 wherein the slurry medium/coal weight ratio is about 1 /l.

Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for at least partially drying coal comprising means for mixing wet coal and slurry medium obtained from coal liquefaction, and flash means operatively connected to said mixing means for vaporizing water from the mixture of coal and slurry medium by subjecting said mixture to a reduced pressure and a temperature below the vaporizing temperature of said slurry medium but above the vaporizing temperature of water.

2. An apparatus according to claim 1 wherein said mixing means is an eductor means.

3. An apparatus according to claim 1 wherein coal grinding means is operatively connected between said mixing means and flash means and/or downstream of said flash means.

4. An apparatus according to claim 1 wherein thickening means is operatively connected downstream of said flash means for removing a part of the slurry medium from the slurry medium/coal mixture issuing from said flash means.

5. An apparatus according to claim 4 wherein coal grinding means is operatively connected downstream of said thickening means. 

1. Apparatus for at least partially drying coal comprising means for mixing wet coal and slurry medium obtained from coal liquefaction, and flash means operatively connected to said mixing means for vaporizing water from the mixture of coal and slurry medium by subjecting said mixture to a reduced pressure and a temperature below the vaporizing temperature of said slurry medium but above the vaporizing temperature of water.
 2. An apparatus according to claim 1 wherein said mixing means is an eductor means.
 3. An apparatus according to claim 1 wherein coal grinding means is operatively connected between said mixing means and flash means and/or downstream of said flash means.
 4. An apparatus according to claim 1 wherein thickening means is operatively connected downstream of said flash means for removing a part of the slurry medium from the slurry medium/coal mixture issuing from said flash means.
 5. An apparatus according to claim 4 wherein coal grinding means is operatively connected downstream of said thickening means. 